The Dutch horticultural sector shows interest in production of microalgae. When microalgae and a tomato crop are produced in the same greenhouse, both shared advantage of and competition for resources will occur. In this study a model was developed to predict algae biomass production in tubular photobioreactors (PBR) and to assess the economic feasibility of combined production of tomatoes and algae. The effects of the location of the PBR in the greenhouse, the diameter of the PBR tubes, the algae biomass concentration, the light intensity and the PBR temperature were considered. The economic feasibility of combined production was calculated, taking into account both investment and running costs. Three possible locations for the PBRs were considered. The most sensitive growth factor influencing economics of the systems was light. Economic feasibility of algae production underneath the tomato crop was poor; a minimum unit biomass production cost of 70 € kg-1 dry matter (DM) was calculated. Increasing the light intensity by decrease of the tomato LAI by extra leaf picking increases economic feasibility of algae production underneath the crop. Economic feasibility of algae production in a separated compartment was computed to be good with a minimum unit biomass production cost of 11 € kg-1 DM. The developed model can function as a basis for further research on combined production of a crop and microalgae in Dutch greenhouses